This study reports the availability of seawater as an economical chloride (Cl⁻) source for the UV/electro-chlorine process from the viewpoints of advanced oxidation performance and unwanted byproduct formation of chlorate ion (ClO₃⁻) and bromate ion (BrO₃⁻). In the electrochemical oxidant production stage, the oxidant production rate in diluted seawater containing 30 mM Cl⁻ was 21% lower than that in the NaCl solution due to coexisting electrolytes in the seawater. The ClO₃⁻ formation during electrolysis was successfully inhibited under acidic conditions and BrO₃⁻ formation was not detected in the diluted seawater. However, ClO₃⁻ and BrO₃⁻ were steadily formed in the undiluted seawater electrolysis, even when the initial pH value was set to 3. The oxidant utilization efficiency for 1,4-dioxane removal during UV irradiation was not deteriorated in the diluted seawater but decreased under basic conditions due to the radical scavenging effect of electrochemically produced free bromine and free chlorine. As a result, the formation of BrO₃⁻ and ClO₃⁻ was enhanced under basic conditions, whereas BrO₃⁻ formation was completely inhibited at an initial pH ≤ 5. Consequently, the diluted seawater was thought to be available as a Cl⁻ source for the UV/electro-chlorine process if an acidic condition was maintained throughout the operation.

Membrane bioreactor-reverse osmosis process (MBR-RO) is widely applied in wastewater treatment, especially when high-quality treated water is needed. Although MBR shows better performances in the removal of pathogens than the conventional activated sludge process, stable operation of RO process in the latter step of MBR-RO depends on residual bacteria in the filtrate of microfiltration membranes. Species and sizes of bacteria found in the filtrate of activated sludge with 0.2 μm pore-size polycarbonate membranes were investigated in this study. Isolated bacterial species grown on R2A agar medium were identified based on the full length 16S rRNA gene sequences. The result showed that approximately 90% of the isolates found in the filtrates were members of phylum Proteobacteria in which Ralstonia spp., Achromobacter spp., Methylobacterium spp. and Methylorubrum spp. accounted for the largest proportions while other bacteria affiliated with phyla Actinobacteria and Firmicutes. The leakage of Ralstonia and Actinobacteria was probably due to their small sizes judging from microscopic observation, while a longer filtration time is needed for Methylobacterium and Methylorubrum to be detected in the filtrate.

Ammonium (NH₄⁺) contamination makes groundwater undrinkable. The dropping nitrification unit, a simple and low-cost biological unit, has been found to be effective for NH₄⁺-removal from contaminated groundwater at a near-neutral pH. However, the pH of groundwater varies widely and is highly alkaline (pH 8.7−10) in some areas of the world, which could negatively affect the biological nitrification process. The objectives of this study were to investigate the NH₄⁺-removal from alkaline groundwater using dropping nitrification units with sponge or biofringe material, compare their removal efficiencies, and characterize the effect of alkaline groundwater on the growth and activity of nitrifying bacteria. Synthetic alkaline groundwater (50 mg-NH₄⁺-N L⁻¹; pH 9.4 ± 0.1) was dropped from the top of 1-m long hanging units at 3 mL min⁻¹ for 56 days. The NH₄⁺-removal efficiency of sponge units (> 88%) was significantly higher than that of biofringe units (56−89%). The abundance of amoA gene of ammonia-oxidizing bacteria increased significantly over 56 days and was significantly higher in sponge units than in biofringe units, resulting in higher NH₄⁺-removal in sponge units than that in biofringe units. This study demonstrated that dropping nitrification units can be used effectively for NH₄⁺-removal from groundwater having a neutral to alkaline pH.